Re: Report - Dimmer as a Variac.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Sharpe by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Terry, All

OUCH!!!    =8*][.  What was surprising to me was the integration (PF) capacitor
made the situation MUCH MUCH worse.

To make a true solid state Variac, it appears that the following conditions
must
be met:
1.  Continuous current flow throughout the AC cycle.
2.  4 quadrant power flow (power to load, load to power line), without blowups
     or excessive EMI/RFI generation.
3.  Continuous power conversion at a considerably higher frequency then line
     frequency, that is forced commutated.  This condition unfortunately
eliminates

     SCR's and Triac phase control from consideration.  Also, significant
tolerance

     to momentary and sustained overloads without catastrophic control or load
     detonation.
4.  Condition 3 allows for high speed response for constant current, constant
     voltage and instantaneous fault conditions.  In fact, constant current
control, with
     voltage as a secondary control loop is an extremely robust controlling
method
     that is finding much industry favor of late.
Several recent power electronics topology circuits have appeared that may
be leveraged to this problem...

Back to the drawing board, let me see what I can come up with (with a
little help
from some colleagues...)

Regards

Dave Sharpe, TCBOR
Chesterfield, VA. USA

> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>
> Hi All,
>
> I wired up the dimmer and hooked it to a 250 watt light bulb and got the
> following voltage waveform:
>
> http://hot-streamer-dot-com/temp/250W-R.gif
>
> The dimmer is holding off the voltage turn on until what appears to be a
> timer triggers it to turn on.  The dimmer remains conducting until the AC
> reaches zero volts (perhaps amps).
>
> I then hooked the input of my small coil in parallel with the 250 watt
> light and tried again:
>
> http://hot-streamer-dot-com/temp/250W-RandSTC.gif
>
> This is the voltage waveform I caught but the 2.5 amp fuse on the coil's AC
> input protection blew right away.
>
> I wired in the Pearson current monitor and tried again with a 4 amp input
fuse:
>
> http://hot-streamer-dot-com/temp/VandI.gif
>
> Looks like I am getting current spikes...  Big ones...  At first I though
> the MOVs where clamping voltage spikes but the fuse is on the other side of
> the MOVs and the peak voltage is lower than the MOV clamp voltage.  Also,
> some of the lower voltage peaks are getting just as big of current spikes.
>
> I clicked the gain down and tried again to see how high the spikes are:
>
> http://hot-streamer-dot-com/temp/VanI-2.gif
>
> Only 58 amps!! =:o
>
> I suspected the 60uF of PFC caps are not getting along with the sudden
> dimmer voltage turn on which is about 180 volts.  So I pulled the
> connectors off the caps to take them out of the circuit and tried again:
>
> http://hot-streamer-dot-com/temp/NoPFC.gif
>
> Neat!  The fuses don't blow and the current and voltage are reasonable now
> :-))  There are still 11.8 amp current spikes which may be due to the
> capacitors in the small coils dual stage line filter:
>
> http://hot-streamer-dot-com/TeslaCoils/MyCoils/SmallCoil/small_ACwiring.jpg
>
> I can hear high voltage on the NST output with just the NST protection
> circuit attached.  The input voltage spikes may be pumping high voltage
> spikes onto the output too.  I will have to hook up the high voltage
> fiber-optics to check that but that may not be a problem once it is hooked
> to a primary cap.
>
> So PFC caps cause big current spikes with he dimmer's sudden turn.  The
> output voltage seem to be mirroring the input signal giving high voltage
> spikes on the NST output at a low power setting on the dimmer.  The line
> filter may be also causing current spikes, but small ones.
>
> Sort of bad not to be able to use PFC caps but the output spikes should not
> be a problem and the line filter perhaps can be moved before the dimmer or
> those spikes just ignored.
>
> Some additional pics of the "stuff" are at:
>
> http://hot-streamer-dot-com/temp/P7070006.jpg
> http://hot-streamer-dot-com/temp/P7070007.jpg
> http://hot-streamer-dot-com/temp/P7070008.jpg
>
> Thanks to Brain for letting me use his fiber probe that I have back here
> for some "factory repairs" ;-))  I left mine on and toasted the batteries...
>
> The science goes on...
>
> Cheers,
>
>         Terry